Feeding The Broodmare: Eating for Two

The optimal feeding program for a broodmare during pregnancy is designed with two primary considerations in mind maintaining the mares health and supporting the growth and development of the fetal foal. Both of these considerations are affected greatly by the rate of fetal growth which varies significantly from early gestation( 0 to 4 months) to midgestation 5 to 8 months to late gestation( 9 to 11 months) also known as the final trimester.
Fetal Growth During Gestation 

During the early months of pregnancy the fetus grows very slowly and so the nutritional requirements of the mare remain similar to those of a nonpregnant mare. Starting in the fifth month of gestation the fetal growth rate begins to increase resulting in corresponding increases in the mares nutrient needs that continue on a monthbymonth basis throughout midgestation. However by seven months the fetus is still very small less than two percent of the mares body weight and only approximately 10 to 15 percent of its weight at birth.
Fetal growth is most rapid in late gestation. During the final trimester the fetal foal growing now at a rate of approximately one pound per day gains about 70 to 75 percent of its birth weight. The fetuss accelerated growth rate and the increased nutrient uptake required to support this growth result in greater demand on the broodmares body.
Energy Protein
A broodmare feeding program is ideally developed with the goal of feeing as much forage as possible while limiting grain intake to the minimum amount required for satisfying the mares energy needs. In early to midgestation good quality forage pasture or hay and a vitaminmineral supplement may be sufficient to meet the mares nutrient requirements and allow her to maintain condition bearing in mind that recommended changes in the dietary level of certain minerals around the fifth month may require adjustments to the size of the daily supplement ration.
Overfeeding a mare in early pregnancy is a common mistake often causing her to become overweight. A body condition score between 5 and 7 according to the Henneke body condition scoring system is considered optimal for a broodmare throughout the pregnancy.
At around the seventh month of pregnancy some mares may require the addition of concentrates to the diet in order to maintain condition as the demands of the fetus increase. Alternatively increasing the grain ration may be avoidable if higher quality forage with a higher caloric and protein content